A Question of Two Batteries

Just changed motorhomes and being 'a bit of a scrooge', I removed the 2nd Leisure battery fitted to my former 2 year old motorhome with a view to using it on the new one. Trouble is, the "older" battery is rated at 100Ah and the battery on the new MH is rated at 90Ah. The batteries are also different makes- although they are both proper camping leisure batteries.
Can anyone tell me how they should be connected and whether they need any fuses (or resistors) between them?

Would I be right in thinking that both batteries, connected as above, would be recharged by a) the engine whilst on the move and b) by the charging unit when hooked up to the mains ?
Also, when in use would both batteries be drained together or one after the other ?
Thanks

Would I be right in thinking that both batteries, connected as above, would be recharged by a) the engine whilst on the move and b) by the charging unit when hooked up to the mains ?
Also, when in use would both batteries be drained together or one after the other ?
Thanks

Make and capacity don't matter.
The charger will only see them as one 190ah battery.
Age, on the other hand, does matter.
If the older one is more than a couple of years old it may have a reduced capacity and will pull the better one down to a reduced capacity as it tries to bring the older back to full capacity when not on charge..

-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-I'm trying to see it from your point of viewbut i cant get my head that far up my ass_-_-_-_-_-_-_-_-_-_-_-_

For the charging to work at best they would both need to be the same type ie. Gel, AGM, or Lead Acid, also the control panel again depending on the make and features may need to be setup for the larger Ah.